Flying Bedstead

Otherwise known as the Rolls-Royce Thrust-Measuring Rig (TMR), an experimental
aircraft that was first flown on Aug. 2, 1954 and used in the early development
of VTOL (vertical takeoff-and-landing) aircraft. The TMR was fitted with
two MK4 Nene jet engines, which were standard Sea Hawk engines modified
only by an air bleed system that allowed 10% of the engine compressor air
to bleed off for the control systems of the rig. The engines faced in opposite
directions to each other at the ends of a tubular construction; the efflux
from the jet pipes – a central one and a bifurcated one from the other
engine – was turned downward through 90°.

Two 95-gallon fuel tanks were fitted under the engines and the whole rig
supported by four hydraulic oleo legs. A platform across the structure above
the engines had a seat bolted to it together with a conventional type control
column and pedals that operated control valves from the engine compressor
air bleed system collector box. The TMR was controlled by bleeding air from
the engine through the control valves to diametrically opposed pipes, each
equipped with a nozzle that could swivel 30° in either direction for
turning the rig left or right. The control valves were also interconnected
to the control column so that movement of the column would restrict the
flow of air to the nozzles, thereby reducing the thrust and so controlling
which direction the rig would go.

The thrust-to-weight ratio of the rig was critical: any vertical take off
(VTO) aircraft must have a engine thrust that's greater than the total weight.
The latter was minimized so as to keep within a 25% thrust advantage. Each
engine provided a thrust of 3,850 lbs, which, added to the 325 lbs thrust
from each of the bleed nozzles, gave a total available thrust of 8,350lbs.
This compared with a total weight for the rig, complete with pilot and full
fuel tanks, of 7,196lbs. Handling improved as fuel was consumed; total running
time was about 15 minutes.

The first rig, called XA314, made an initial ground run on Jul. 3, 1953
before first attempting to lift off the ground on Jul. 6, piloted by wing-commander
Harvey Hayworth, Rolls Royce chief test pilot. The rig lifted only to the
full extent of the hydraulic oleo legs so that the wheels did not actually
leave the ground. During these early days of testing, it was felt that for
safety's sake the rig should be tethered; consequently, a large gantry was
built and cables attached to either side and above the rig from cable drums
built into the gantry. After 20 hours testing the rig was withdrawn on Nov.
19, 1953 for extensive modifications and overhaul inspection of the engines.

After several months in the workshops the rig was rolled out again, put
under the gantry, and a tethered flight carried out to test the new modifications.
These were so successful that preparations were made for the first free
flight. This took place on Aug. 3, 1954, and was piloted by Capt. Ron Shepherd
before a distinguished audience. The rig rose slowly into the air and was
held steady in a hover attitude. It then moved forward, made a circuit of
the test area was made, and demonstrated sideways and backwards movements
before successfully landing. During the next four months a number of free
flights were made, all at a height of 13-15 ft. but one flight was made
up to 50ft. to ensure that there was no ground effect influencing the rig.
The final flight took place on the Dec. 15, 1954. The rig was then transferred
from Derby to Farnborough. A second rig, the XA426, was built and first
flown on Oct. 17, 1955. It conducted extensive tethered flying for 12 months
before its first free flight on Nov. 12, 1956. This rig crashed a year later
on Nov. 28, 1957, killing the pilot. Testing of the TMR subsequently ceased
at Rolls Royce.